As an example, a wiring board may be provided with through holes by press work or drill work. An electronic part such as a capacitor may be accommodated inside the through holes of the wiring board. The through holes formed by the press work or the drill work penetrate the wiring board in its thickness direction while maintaining a substantially constant opening area (a through hole having a longitudinal cross-sectional shape other than a tapered shape). In the manufacturing process of the wiring board, for example, a mounter for an electronic part may be used to accommodate the capacitor or the like into the inside of the through hole as disclosed in Japanese Laid-open Patent Publication No. 2011-216740.
However, it is not easy to accommodate the electronic part inside the through hole penetrating the wiring board in the thickness direction while maintaining the substantially constant opening area. Said differently, if a mounter having a high accuracy is used to accommodate the electronic part, the electronic part is accurately mounted into the through hole. If a mounter having a low accuracy is used to accommodate the electronic part, the electronic part is not accurately mounted into the through hole. Specifically, there are problems that an electronic part is obliquely accommodated into a through hole, an electronic part is not accommodated into a through hole because of being prevented from being inserted into the through hole (the electronic part contacts an edge of the through hole so as to be dropped off), and so on.